The post- September 11 release of anthrax spores resulted in five civilian deaths, eighteen infections, and required that more than 30,000 individuals undergo prophylactic antibiotic therapy. This event also highlighted the need for a more thorough understanding of the pathogenesis of anthrax, and improved vaccines that would be appropriate for pre- or post-exposure immunization of civilian and military populations. The interaction of macrophages with one of the principal toxins produced by Bacillus anthracis, Lethal Toxin, has been a primary focus of laboratories studying the pathogenesis of this organism. However, we now know that dendritic cells are important sentinel cells distributed throughout the body that play a major role in detecting invading pathogens and in the initiation of the host immune response to foreign antigens. Our preliminary studies have shown that anthrax toxin affects cell signaling pathways and cytokine expression in toxin-treated dendritic cells. We will test the hypothesis that anthrax toxin targets several unknown but key molecular pathways within the dendritic cell that disarm its critical function in host-pathogen defense. The first specific aim is to determine the molecular changes within dendritic cells treated with anthrax toxin. We will use both gene microarray analysis and traditional cell signaling kinase assays to learn about both genomic and proteomic changes elicited by toxin treatment of these cells. The second aim is to determine the changes in cytokine expression profiles by dendritic cells treated with anthrax toxin. This will be measured by cytometric bead arrays, ELISA and RNase protection assays and is used here to reveal how the anthrax toxin-treated dendritic cell might affect other host cells and in particular those involved in host immune responses. This combined approach will significantly advance our understanding of B. anthracis pathogenesis in two ways: it will elucidate the dendritic cell's role in B. anthracis pathogenesis and it will lead to the identification of new cellular targets of anthrax toxin. Moreover, because of the critical role that dendritic cells play in initiating the host immune response, the proposed studies may lead to the development of improved vaccines against anthrax. This body of information will also serve as the foundation for new research areas to explore in future proposals.